Utilising pathway engineering in shaping a synthetic microbial consortium for municipal wastewater treatment

While activated sludge systems are in common use for municipal and industrial wastewater treatment, relatively little research has focused on engineering the microbial community responsible for degrading organic pollutants in wastewater. One key challenge that needs to be overcome in defining a synthetic microbial community for wastewater treatment systems lies in the dynamic nature in which microbial community structure adapts to changing environmental and nutritional conditions, as well as influent microbial compositions. In particular, the latter condition poses a significant challenge to defining a synthetic microbial consortium for municipal wastewater treatment systems as compared to those for industrial wastewater treatment since microbial load in influent of industrial wastewater is low. Given that a synthetic microbial consortium provides a means for optimizing wastewater treatment performance at the molecular and metabolic pathway level in what is a systems biology problem, careful selection of microbial species to constitute a microbial community for degrading pollutants in wastewater would be the first step. But, moving beyond use of wild-type species for wastewater treatment lies the opportunity to use the tools of metabolic engineering and synthetic biology to endow microbes in wastewater treatment with newfound capabilities that would help ensure treatment success in dynamically changing influent, environmental and nutritional conditions. To this end, pathway engineering might help distribute the load of degrading organic pollutants between two non-antagonistic microbial species in a consortium. This need arises due to the frequent accumulation of toxic metabolites and intermediates during degradation of organic pollutants particularly in treating industrial wastewater. Another avenue for engineering microbes for wastewater treatment concerns the ability of microbial species to extract maximum energy content and carbon building block during degradation of organic compounds. Specifically, mineralization of organic pollutants to carbon dioxide would provide an ideal solution from the environmental protection perspective, but this is hard to achieve at the pathway level, hence the need for engineering high energy yielding pathway with evolved enzymes for pollutant degradation. In addition, engineered strains should have high growth rates to remain competitive with microbes in wastewater influent; however, growth rates must be modulated to reduce biomass formation as sludge treatment constitute a cost to wastewater treatment. Overall, engineering a synthetic microbial community for activated sludge municipal and industrial wastewater treatment would help resolve vulnerability of current systems to treatment upsets. But, given the increasing trend of recycling treated secondary effluent for non-potable reuse, need exists for certifying the use of engineered microbes with heterologous genes integrated into the genome through conducting a battery of assays to determine whether engineered strains would constitute a risk to environmental microbes through fast growth rates and out-competition of nutrients.